The present invention relates to systems for analyzing the power distribution of an input signal as a function of frequency and, in particular, to such systems of the sweeping frequency spectrum type. Various arrangements have been proposed for sweep frequency analyzers. Prior arrangements of the heterodyne type beat the incoming signal to a higher frequency, and pass the heterodyned signal through one or more narrow bandwidth filters, such as filters of the third octave type. This arrangement eliminated the reading of harmonics of the input signal, but the resolution of these arrangements was poor, since the filters still had a bandwidth response of a few hertz. Further, such filters had poor transient response and slow scanning rate, owing to their high Q rating.
A second major type of frequency spectrum analyzer, the digital type, typically performs a Fast Fourier Transform (FFT) on the incoming time-based signal. Such processing is not continuous in that digital systems typically employ a sampling process, which is undesirable in many applications where the entire incoming signal must be analyzed. Further, such digital systems, though very rapid, do not operate in true real time since the FFT must be performed on a stored signal and since they perform an analysis of a repetitive event by a sampling process. It is desirable in many instances to perform a continuous analysis of the incoming signal with the time sequence of the events preserved between input and output. Such performance is possible only with a real time analyzer. None of the systems heretofore available have been found to provide an accurate absolute measurement of frequency component amplitudes.
It is therefore an object of the present invention to provide an improved sweep frequency analyzer which performs an accurate absolute frequency strength measurement in real time.
It is another object of the present invention to provide a highly sensitive sweep frequency analyzer having a continuous high resolution measuring capability.
Yet another object of the present invention is to provide a sweep frequency analyzer having a faster scanning rate than prior art analog analyzers.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.